fix: close Chromium tabs on crawler fetch error paths

new_page() opened a tab that was only closed on the happy path; a `?` on
wait_for_nav / content() leaked it (chromiumoxide doesn't close on drop),
so errored fetches accumulated tabs in the shared browser. Add a generic,
unit-tested `close_after(close, body)` helper and wrap the three fetch
sites (chapter content, session probe, source navigate) so the tab is
closed on every exit path — including navigate's content()-read branch,
which previously leaked.

Bump to 0.124.5.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/src/crawler/content.rs

@@ -122,22 +122,31 @@ async fn fetch_chapter_html_once(
         .new_page(source_url)
         .await
         .with_context(|| format!("open chapter page {source_url}"))?;
-    crate::crawler::nav::wait_for_nav(&page)
-        .await
-        .context("wait for chapter nav")?;
-    // Best-effort wait for the reader marker — same partial-render
-    // race that bit the chapter-list parser can hit here. Timeout is
-    // not an error; the chapter probe + parser sentinels still catch
-    // real failures.
-    let _ = crate::crawler::nav::wait_for_selector(
-        &page,
-        "a#pic_container",
-        crate::crawler::nav::SELECTOR_TIMEOUT,
+    // Close the tab on every exit path — a `?` on wait_for_nav / content()
+    // would otherwise leak it (chromiumoxide doesn't close on drop).
+    let closer = page.clone();
+    crate::crawler::nav::close_after(
+        async move {
+            closer.close().await.ok();
+        },
+        async {
+            crate::crawler::nav::wait_for_nav(&page)
+                .await
+                .context("wait for chapter nav")?;
+            // Best-effort wait for the reader marker — same partial-render
+            // race that bit the chapter-list parser can hit here. Timeout is
+            // not an error; the chapter probe + parser sentinels still catch
+            // real failures.
+            let _ = crate::crawler::nav::wait_for_selector(
+                &page,
+                "a#pic_container",
+                crate::crawler::nav::SELECTOR_TIMEOUT,
+            )
+            .await;
+            page.content().await.context("read chapter html")
+        },
     )
-    .await;
-    let html = page.content().await.context("read chapter html")?;
-    page.close().await.ok();
-    Ok(html)
+    .await
 }
 
 /// Pure-over-IO loop: fetch + classify, up to `max_attempts` total